There have been known image projection devices that project an image by scanning a light beam emitted from a light source in the main scanning direction and the subscanning direction by a scan mirror. In such image projection devices, when the oscillation of the scan mirror and the emission timing of the light beam from the light source deviate from each other, the image quality deteriorates. Thus, a method of correcting the emission timing of the light beam from the light source has been suggested (e.g., see Patent Documents 1 and 2).
There have been also known image projection devices that directly project an image onto the retina of the user. Patent Document 1 directly projects an image onto the retina by scanning a light beam emitted from the light source by a scan mirror and projecting the scanned light onto the retina of the user. In Patent Document 1, the light beam extracted by a half mirror provided in the subsequent stage of the scan mirror is detected by a light detector, and the emission timing of the light beam from the light source is corrected based on the detection result to reduce the deterioration of the image quality.